Mechanically actuated fuel injectors typically have a fuel pressurizer that includes a plunger that is driven to reciprocate by a cam rotated by an engine. The fuel pressurizer can be in a separate body from the fuel injector, such as in a unit pump. However, more typically, the fuel pressurizer and injection nozzle are carried in a common injector body. Some electronic control was initially introduced to these fuel injection systems by including an electronically controlled spill valve. In other words, as the cam rotates, fuel pressure does not develop in the fuel injector until the spill valve is closed. When the spill valve is open, fuel displaced by downward movement of the plunger is merely recirculated back to tank.
As the demands for ever more flexible fuel injection rate shapes have grown, and better control over timing arrived, these fuel injection systems were further improved by incorporation of electronic control over movement of the nozzle needle valve member. Such a fuel injector is shown, for example, in co-owned U.S. Pat. No. 6,279,843 to Coldren et al. These fuel injectors have demonstrated the ability to produce a variety of different fuel injection profiles at least in part by varying the relative timing of electronically opening and closing the spill valve relative to the energization and de-energization of the electrical actuator controlling a needle control valve. Depending upon the position of the needle control valve, pressure is either applied or relieved to a closing hydraulic surface associated with the nozzle needle valve member. In a typical injection event, the cam rotates, the spill valve is closed via a first electrical actuator, and then injection is initiated by energizing a second electrical actuator to relieve pressure on the closing hydraulic surface of the needle valve member. There remains room for improvement over these fuel injection systems.
In certain rare circumstances, these fuel injection systems have the potential for becoming overpressurized in a way that could possibly lead to injector as well as engine damage. For instance, it is possible for the electrical circuitry associated with the needle control valve to fail while the electrical circuitry associated with spill control remains active. In such circumstances, it is possible for the fuel injector to become pressurized in a typical manner by electronically closing the spill valve; however, no injection is able to occur since a failure in the electronics for the needle control valve prevent the nozzle from opening, since the electronic failure prevents energization of a second electrical actuator to relieve pressure on the closing hydraulic surface of the needle valve member. As such, the plunger will continue its downward movement, but the fuel in the fuel injector will have nowhere to go. In these rare circumstances, tip breakage can occur or the linkage between the rotating cam and the injector tappet can become overstressed and break. In any event, this potential failure mode can possibly result in catastrophic engine failure if even one fuel injector becomes overpressurized and its tip breaks off into an engine cylinder.
The present disclosure is directed to overcoming one or more of the problems set forth above.